1. Field of the Invention
The present invention relates to a single-chip microcomputer including a nonvolatile semiconductor memory device with a dynamic burn-in test function and its dynamic burn-in testing method.
2. Description of the Related Art
Generally, in order to reveal defective single-chip microcomputers resulting from time and stress due to inherent defects or manufacturing fluctuations, a burn-in test screening method is carried out at a stage of testing before shipment. As typical burn-in test screening methods, there are a static burn-in test screening method, a clocked burn-in test screening method and a dynamic burn-in test screening method.
In a static burn-in test screening method for a single-chip microcomputer in a high temperature state, all input/output terminals are made to be at special levels, and power supply voltages are supplied to power supply terminals. In the static burn-in test screening method, since the single-chip microcomputer is not operated, stress is not equally applied to the elements of the single-chip microcomputer, so that only a small burn-in test screening effect is obtained.
In a clocked burn-in test screening method for a single-chip microcomputer in a high temperature state, only clock signals required for operating the single-chip microcomputer are supplied thereto, so that the single-chip microcomputer carries out special operations. Also, in the clocked burn-in test screening method, since the operation of the single-chip microcomputer is limited, stress is not equally applied to the elements of the single-chip microcomputer, so that only a small burn-in test screening effect is obtained.
In a dynamic burn-in test screening method for a single-chip microcomputer in a high temperature state, various kinds of voltages are supplied to input terminals while usual power supply voltages or higher power supply voltages are supplied as power supply voltages. As a result, the single-chip microcomputer is operated, so that data are generated at output terminals and are compared with expected data. Thus, in the dynamic burn-in test screening method, since the single-chip microcomputer is actually operated, stress is equally applied to the elements of the single-chip microcomputer, so that the burn-in test screening effect can be enhanced.
In a prior art dynamic burn-in test system for a single-chip microcomputer incorporating a nonvolatile semiconductor memory such as a flash electrically-erasable programmable read-only memory(EEPROM), the single-chip microcomputer is also constructed by a write circuit for writing data into the flash EEPROM, a read circuit for reading data from the flash EEPROM, and an erase circuit for performing a flash erase operation upon the flash EEPROM.
In the above-described prior art dynamic burn-in test system, when carrying out a dynamic burn-in test, a large scale integrated (LSI) tester directly controls the write circuit, the read circuit and the erase circuit, so as to perform a write operation, a read operation and a flash erase operation upon the flash EEPROM, respectively. Then, when the read circuit receives a read instruction from the LSI tester, one word of data is read from the flash EEPROM to the LSI tester, so that the LSI tester compares the read word of data with expected data, thus carrying out a verification, i.e., determining whether the flash EEPROM, the write circuit, the read circuit and the flash erase circuit are normal. Also, in order to enhance the burn-in test screening effect without increasing the number of signals supplied to the single-chip microcomputer, test programs are stored in the flash EEPROM in advance, so that all the internal circuits in the single-chip microcomputer are operated, i.e., stress is applied to all the internal circuits as equally as possible. This will be explained later in detail.
In the above-described prior art burn-in test system, however, the flash EEPROM is required to be large in size, and the burn-in screening effect deteriorates. Further, the LSI tester is high in manufacturing cost. This also will be explained later in detail.